Preparation of 0-aryl 0,0-dialkyl phosphorothioates

ABSTRACT

0-Aryl 0,0-dialkyl phosphorothioates are prepared by a method which comprises reacting in an organic solvent-water reaction medium, one molecular proportion of an 0,0di(loweralkyl)phosphorochloridothioate with one molecular proportion of a phenolic compound. These compounds are useful as pesticides.

United States Patent Kroposki et al.

[ Jan. 21, 1975 PREPARATION OF O-ARYL 0,0-DIALKYL PHOSPHOROTHIOATES Inventors: Lorraine M. Kroposki, Walnut Creek, Calif.; Masao Yoshimine, Midland, Mich.

The Dow Chemical Company, Midland, Mich.

Filed: Mar. 28, 1973 Appl. No.: 345,583

Assignee:

US. Cl. 260/973, 260/964 Int. Cl. C07f 9/18 Field of Search 260/973 References Cited UNITED STATES PATENTS 3/1960 Tabor 260/973 Schrader et al 260/973 Hanna 260/973 Primary Examiner-Lorraine A. Weinberger Assistant ExaminerRichard L. Raymond Attorney, Agent, or Firm-S. Preston Jones ABSTRACT 4 Claims, N0 Drawings 1 PREPARATION OF O-ARYL 0,0-DIALKYL PHOSPHOROTI-IIOATES PRIOR ART AND BACKGROUND OF THE INVENTION Several methods of preparing the O-aryl 0,0-dialkyl phosphorothioates are known. In one method, the compounds may be prepared by the reaction of an O-aryl phosphorodichloridothioate and an alkali metal alcoholate or by the reaction of an 0,0-dialkyl phosphorochloridothioate and an alkali metal phenolate. The contacting of the reactants in such methods is carried out in an inert organic solvent and at a temperature of from about to 80C. When operating in accordance with such methods, the O-aryl 0,0-dialkyl phosphorothioates are obtained in yields of about 55 percent or less. In still another method, the mixed phosphorothioate esters may be prepared in yields of about 75 percent by the reaction of an 0,0-dialkyl phosphorochloridothiate with an aqueous solution of a sodium phenolate in the presence of a copper catalyst.

Another method is taught in U.S. Pat. No. 2,928,864 wherein one molecular proportion of 0,0- di(loweralkyl)-phosphorochloridothioate is reacted in the absence of a catalyst and at a temperature of from 40 to 70C. with from 1 to 1.5 molecular proportions ofa phenolic compound. This reaction is carried out in the presence of an alkali metal hydroxide and water. This method has enjoyed some success but suffers from low product yields and purity when the phosphorous and phenolic compound reactants are employed in equimolar proportions. While high product yields are obtained when employing the phenolic reactant in molar proportions greater than one mole per mole of phosphorous reactant, the problems associated with the use of these higher proportions do not make this process overly attractive. A high phenolic waste byproduct production is one of the major problems associated with the use of larger amounts of the phenolic reactant. This phenolic waste interferes with the purity of the desired product and increases the cost of preparing a high purity product. In addition, the phenolic waste must be treated to recover the phenolic starting material since its disposal, by conventional means, constitutes an ecological problem. Further, the recovery of the phenolic compound is necessary because of the high cost of this reactant. One method of recovery employed has been to acidify the aqueous phenolic reaction medium after product recovery recovering the regenerated phenolic compound therefrom and recycling it. This solution while effective in recovering some of the phenolic starting material, adds to the problem by requiring the handling of strong and corrosive acids and the disposal of the spent acid. A more economical method for the production of O-phenyl 0,0-dialkyl phosphorothioate esters in superior yields and in high purity would be very desirable.

SUMMARY OF THE INVENTION It has now been found that O-aryl 0,0-di(loweralkyl)phosphorothioate esters corresponding to the formula employed. When the process of U.S. Pat.

wherein X represents chloro or bromo; n represents an integer of from O to 3 and R represents loweralkyl of from 1 to 5 carbon atoms can be prepared by a method which comprises reacting, in the presence of an organic solvent-water reaction medium, equimolar amounts of an 0,0-di(lower-alkyl)phosphorochloridothioatc with phenol or a bromo or chloro substituted phenol (hereinafter called phenolic compound or reactant) at a temperature of from about 10 to about C. This reaction is further carried out under alkaline conditions by the addition of an alkali metal hydroxide or a mixture of an alkali metal hydroxide and boric acid to maintain the pH of the reaction mixture at about 8 to about 13 and preferably at 10.5 to 11.5.

In the present specification and claims, the term "alkali metal refers to the metals sodium, potassium, lithium, cesium and rubidium. The term loweralkyl refers to alkyl radicals of 1 to 5 carbon atoms such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl,

secondary butyl, tertiary butyl and amyl.

The present method is an improvement over the method taught in U.S. Pat. No. 2,928,864 in that higher yields of high purity product are obtained when employing equimolar amounts of the reactants and the problems of disposing of excess phenolic compounds are avoided since no excess of the phenolic reactant is No. 2,928,864 is carried out employing equimolar amounts of the reactants the yield of the product is low and the purity of the product is also low. By practicing the present improved method, the yield of the product is as high as that obtained when employing greater than equimolar amounts of the phenolic reactant without the concurrent problems of phenolic disposal or'phenol recovery. The present method is also more economical and as stated hereinbefore, gives a product of very high purity. I

The critical feature of the present improved method is in the use of an organic solvent-water reaction medium for carrying out the reaction. The water is usually present in an amount of from about 1 to about 3 moles per mole of the combined phosphorous and phenolic reactants and preferably from about 1 to 2 moles per moleof the combined reactants. The solvent is usually present in an amount of from about 0.1 to 2 moles of the solvent per mole of the combined phosphorous and phenolic reactants and preferably in the range of from about 0.5 to about 1.5 moles per mole of the combined reactants.

Suitable water-immiscible or substantially waterimmiscible organic solvents which may be employed include xylene, cyclohexane, benzene, toluene, chloroform, chlorobenzene, methylene chloride, and nitrobenzene. The preferred solvent is methylene chloride,

In practice, usually the water and the alkali metal hydroxide are employed in the form of an aqueous solution with thealkali metal hydroxide being present in an amount sufficient to maintain the pH of the reaction mixture between about 8 and about 13. This aqueous solution contains from about 10 to about 50 percent alkali metal hydroxide. It is important to maintain the pH of the reaction mixturewithin the above range so as to insure the realization of, the desirable results of the present invention.

Alternatively, the alkali metal hydroxide first can be reacted with the phenolic reactant to convert it to the alkali-metal salt. This reaction can be carried out by contacting the phenolic compound with the alkali metal hydroxide at a temperature of from about 50 to about 60C. The water, solvent and phosphorous reactants are thereafter added and the reaction proceeds as and preferably between about 40 and about 80C. The rate at which the formation ofthe phosphorothioic acid esters takes place has been found to vary with the temperature employed; the longer periods being employed at the lower temperatures. At temperatures in excess of hereinafter set forth. 5

Representative phosphoroehloridothioate reactants h iling point f the Organic solvent, the reaction include 0.0-dimethyl phosphorochloridothioate, 00- h d be ri d ut und r pre s re a e atm diethyl phosphorochloridothioate, 0,0-di-n-propyl spheric pressure, whereas when operating below the phosphorochloridothioate, 0.0-di-ispropyl phosphoroboiling P int Of the rgani vent am ient atmochloridothioate, 0,0-di-n-butyl phosphorochloridothiol0 PheriC pressure is employed. When operating within ate, 0,0-di-sec-butyl phosphorochloridothioate, (),()-dithe preferred temperature limits. reaction times of 0.5 t-butyl phosphorochloridothioate and 0,0-diamyl to 24 hours, preferably l to hours are sufficient for phosphorochloridothioate. practical completion.

Representative phenolic reactants include among Upon the completion of the reaction. the reaction others phenol, 2-chlorophenol, Z-bromophenol, 4- l5 mixture is cooled to room temperature and the organic chlorophenol, 4-bromophenol. 2,4-dichlorophenol, phase separated from the aqueous phase. The organic 2,4-dibromophenol, 3-chlorophenol, 3-bromophenol, phase is washed with dilute alkali metal hydroxide solu- 3,4-dichlorophenol, 3,4-dibromophenol. 2,5- tion followed by water washing. The solvent is removed dichlorophenol, 2,4,5-trichlorophenol, 3,4,5- by evaporation under reduced pressure leaving the detrichlorphenol, 2,4,5-tribromophenol and 3,4,5- sired product. tribromophenol or the alkali metal salts of these phenolic Compounds DESCRIPTION OF SOME PREFERRED Representative compounds which can be prepared EMBODIMENTS y the Process disclosed and Claimed herein, include In order that the present invention may be more fully among others, understood, the following examples are given primarily im hyl -ph ny PhOSPhOIOthIOaIE; by way of illustration and should not be construed as th .0-dimethyl -(m and br0m ph ny limitations upon the overall scope of the present invenphosphorothioates; i

the 0,0-dimethyl 0-(mono-, diand triehlorophenyl)- phosphorothioates; EXAMPLE I 0,0-diethyl O-phenyl phosphorothi a A solution consisting of 39.6 grams (200 millimoles) the 0.0-diethyl -(m0n0-. diand tribromophenyUP- of 2,4,5-trichlorophenol and 8.6 grams (210 millih Ph I' Ihi a moles) of a 20 percent sodium hydroxide solution was the i y (Hmono'i and p yhp heated at 55C. for one (I) hour and cooled at 33C. OSPhOI'OIhiOaIBS; 35 Thereafter 30 milliliters of methylene chloride was -P y phosphorothioate; added to this mixture. To this mixture was added dropthe -P py and tribromophenwise 33.6 grams (200 millimoles) of on- YUP P dimethylphosphorochloridothioate over a period of 14 the 0,0-di-n-propyl 0-(m and trichlorophenminutes. The mixture was thereafter heated at 53C. YUP P 40 for 6.75 hours while maintaining the pH at II by the the 0,0-di-isopr0pyl 0-( and ri hl r p dropwise addition of a 50 percent sodium hydroxide yl)phosphorothioates; solution. At the end of this period, the reaction mixture 0,0-di-n-butyl O-phenyl phosphorothioate; was allowed to cool to room temperature and the orthe 0,0-di-n-butyl and i r m ph nylganic phase separated from the aqueous phase. The or- )PhOSPhOYOIhiOQIeS; ganic phase was washed with 100 milliliters of a 5 perthe 0.0-di-n-butyl -t and trichlorophenylcent sodium hydroxide solution followed by a wash )phosphorothioates; with 100 milliliters of water. The methylene chloride 0,0-di-sec-butyl O-phenyl phosphorothioate; was removed by evaporation under reduced pressure. the 0,0-di-sec-butyl O-(mono-, diand trichlorophen- The 0,0-dimethyl 0-2,4,5-trichlorophenylphosphoroyllph ph hi thioate product was recovered in a yield of 58.6 grams 0,0-di-t-butyl O-phenyl phosphorothioate; (91.6 percent of theoretical) and was found to be 98.9 the 0,0-di-t-butyl O-(mono-, diand tribromophenyl)- percent e,

phosphorothioates; the 0,0-di-t-butyl 0-(mono-, diand trichlorophenyl)- EXAMPLE phosphorothioates; Additional runs were carried out following the proceand the 0,0-diamyl O-(mono-, diand trichlorophenydures of Example l employing the same reactants and l)phosphorothioates. same solvents but using different temperatures and/or The present process is normally carried out at a temreaction times. The results of these runs are summaperature of from between about 10 and about 120C. rized in Table l which follows:

TABLE I Run Amount of Amount of Water Methylene Reaction Temperature Percent Purity of reactant reactant added chloride Time in in C. yield of DMTCP A added in B added in ml. added in hours DMTCP product mm. (a) in mm. (b) (c) ml. (d) product (e) (f) TAB LE l Continued Run Amount of Amount of Water Methylene Reaction Temperature Percent Purity of reactant reactant added chloride Time in in C. yield of DMTCP A added in B added in ml. added in hours DMTCP product mm. (a) in mm. (b) (c) ml. (d) product (e) (f) (a) Amount of sodium trichlorophenate reactant added in millimoles.

(b) Amount of 0.0-Dimethyl phosphorochloridothioate reactant added in millimoles.

mixture. (d) Milliliters of methylene chloride added to reaction mixture.

(c) Milliliters of water added to reaction thioate;

0,0-di-n-propyl O-(2,4-dibromophenyl)phosphorothioate;

0,0-di-isopropyl O-( 3,4,5-trichlorophenyl )phosphorothioate;

0,0-di-n-butyl O-phenyl phosphorothioate;

0,0-di-n-butyl 0-(3-bromophenyl)phosphorothioate;

0,0-n-butyl 0-(2,5-dichlorophenyl)phosphorothioate;

0,0-di-sec-butyl O-phenyl phosphorothioate;

0,0-di-sec-butyl O-(3-chlorophenyl)phosphorothioate;

0,0-di-t-butyl O-phenyl phosphorothioate;

0,0-di-t-butyl O-(4-chlorophenyl)phosphorothioate;

0,0-di-t-butyl O-(2,4,5-tribr0mophenyl)phosphorothioate;

and 0,0-diamyl 0-(2,4,5-trichlorophenyl)phosphorothioate.

What is claimed is:

1. In the process for preparing 0,0-di- (loweralkyl)phosphorothioate esters corresponding to the formula S ll X 8 0-1 4012) wherein X represents chloro or bromo; n represents an integer of from 0 to 3 and R represents loweralkyl of from I to 5 carbom atoms wherein equimolar amounts of a 0,0-di(loweralkyl)phosphorochloridothioate and phenol or a chloro or bromo substituted phenol are reacted at a temperature of from about 10 and about 120C. and at a pH of from about 8 to about l3. the improvement which comprises carrying out the reaction in the presence ofa reaction medium consisting of from about 1 to about 3 moles of water per mole ofthe combined phosphorochloridothioate and phenolic reactants and from about 0.1 to about 2 moles of a water immiscible organic solvent per mole of the combined phosphorochloridothioate and phenolic reactants and thereafter recovering the 0,0-di(loweralkyl)phosphorothioate ester so producedv 2. The process as defined in claim 1 wherein the organic solvent is methylene chloride.

3. The process as defined in claim 2 wherein the phenol reactant is 2,4,5-trichlorophenol and the phosphorochloridothioate reactant is 0,0-dimcthyl phosphorochloridothioate.

4. The process as defined in claim 3 wherein the pH is maintained in the range of from 10.5 to 11.5 and the temperature is between about 40 and about C. 

2. The process as defined in claim 1 wherein the organic solvent is methylene chloride.
 3. The process as defined in claim 2 wherein the phenol reactant is 2,4,5-trichlorophenol and the phosphorochloridothioate reactant is 0,0-dimethyl phosphorochloridothioate.
 4. The process as defined in claim 3 wherein the pH is maintained in the range of from 10.5 to 11.5 and the temperature is between about 40* and about 80*C. 